The retinoic acid receptor-related orphan nuclear receptor (ROR) RORγ and its isoform RORγt (collectively “RORγ/γt”) play a major role in regulation of a variety of biological systems. To illustrate, RORγt has a central role in immune system development, homeostasis, and responses to microbial pathogens. For example, RORγt is required for the differentiation of Th17 cells (Ivanov, I I et al. Cell, 2006, 126, 1121-33), a subset of T helper cells that protect the host from infection by secreting inflammatory cytokines such as IL-17, IL-17 (also called IL-17A), IL-17F, IL-22, and TNFα. These cytokines are signaling proteins that have been shown to be essential in regulating numerous immune responses, including inflammatory responses to antigens. Th17 cells have also recently been shown to have important roles in activating and directing immune responses in a variety of autoimmune diseases, such as experimental autoimmune encephalomyelitis (EAE), collagen-induced arthritis (CIA), inflammatory bowel disease (IBD), cancer (Weaver, C. et al. Ann. Rev. Immunol., 2007, 25, 821-52; Kryczek, I. et al. J. Immunol., 2007, 178, 6730-3; Cua, D. J. et al. Nature, 2003, 421, 744-8; Langrish, C. L. et al. J. Exp. Med., 2005, 201, 233-40; Yen, D. et al. J. Clin. Invest., 2006, 116, 1310-6), and graft-versus-host disease (Carlson, M. J. et al. Blood, 28 Oct. 2008. [Epub ahead of print]; Kappel, L. W. et al. Blood, 17 Oct. 2008. [Epub ahead of print]). Th17 cells have also been implicated in asthma, psoriasis, rheumatoid arthritis, multiple sclerosis (Tzartos, J. S., et al. Am. J. Pathology, 2008, 172, 146-55; Yu, J. J., and Gaffen, S. L. Front. Biosci., 2008, 13, 170-77; and Zheng, Y. et al. Nature, 2007, 445, 648-51), and Crohn's disease (Duerr, R. H., et al. Science, 2006, 314, 1461-63). Additionally, it has been shown that mice defective for expression of RORγt lack Th17 cells and are resistant to a variety of autoimmune diseases and that the absence of Th17-producing microbiota in the small intestine of mice alters the Th17: regulatory T (Treg) cell balance with implications for intestinal immunity, tolerance, and susceptibility to inflammatory bowel diseases (Ivanov, I. I. Cell Host & Microbe, 2008, 4, 337-49).
The formation of immune cell aggregates, such as cryptopatches (CP) and isolated lymphoid follicles (ILF), which contain RORγt expressing cells, is known to be a vital step in many immune responses. For example, CPs and ILFs are required for mucosal immunity and for production of the intestinal antibody IgA. Such immune responses can result in inflammation in various diseases, such as Crohn's disease. The ability to inhibit such immune responses by inhibiting the formation of immune cell aggregates may offer another way to treat diseases associated with such responses.
T-cells have also been demonstrated to play a role in diseases characterized by bone loss and degradation, such as osteoarthritis. For example, in autoimmune arthritis, activation of T cells results in bone destruction mediated by osteoclasts. Th17, whose differentiation is regulated by RORγt, has been shown to be osteoclastogenic, thus linking T cell activation and bone resorption (Sato, K. et al. J. Ex. Med., 2008, 203, 2673-82). Thus, the ability to regulate Th17 cell differentiation via RORγt modulation may offer a way to treat bone loss and degradation, such as that associated with autoimmune disease. Furthermore, interferon gamma (IFN-γ) suppresses osteoclast formation by rapidly degrading the RANK adaptor protein TRAF6 in the RANK-RANKL signaling pathway, and RORγt has been shown to down-regulate the production of IFN-γ (Ivanov, I. I. et al. Cell, 2006, 126, 1121-33). Thus, the ability to regulate osteoclast formation through modulation of RORγt-mediated IFN-γ osteoclast suppression may provide additional methods to treat bone loss and degradation, such as that associated with autoimmune disease (e.g., osteoarthritis).
Circadian rhythm relates to an approximately daily periodicity in the biochemical, physiological or behavioral processes of living beings, including plants, animals, fungi and some bacteria. Members of the ROR family of orphan nuclear receptors have been implicated in regulation of control of circadian clock function by regulation of clock genes (Ueda, H. R. et al. Nature, 2002, 418, 534-39; Sato, T. K. et al. Neuron, 2004, 43, 527-37), and RORγ/γt has been implicated in the regulation of genes that govern circadian metabolism (Kumaki, Y. et al. PNAS, 2008, 105, 14946-51; Liu, C. et al. Nature, 2007, 447, 477-81). Moreover, RORγ gene expression is known to oscillate in a circadian manner in metabolically active tissues such as liver and brown adipose tissue (Yang, X. et al., Cell, 2006, 126, 801-10), which further confirms that a role exists for RORγ in regulating circadian function. Hence, the ability to modulate RORγ/γt expression may also result in circadian rhythm regulation and treatment of disorders associated with disruption of circadian rhythm. Since circadian rhythm is integral in maintaining metabolic levels, whose imbalance is linked to obesity and diabetes, modulators of RORγ/γt may also be useful in treating obesity and diabetes through regulation of circadian rhythm.
In view of the above, a need exists for therapeutic agents, and corresponding pharmaceutical compositions and related methods of treatment that address conditions causally related to RORγt activity, and it is toward the fulfillment and satisfaction of that need, that the present invention is directed.